Liquid crystal displays are display devices that use liquid crystal compositions for display. Liquid crystal displays are used as display devices in a variety of devices, and specifically used as information display devices and image display devices.
Such a liquid crystal display forms an image by transmitting/intercepting light region by region according to an applied voltage. Therefore, external light is needed to form an image on the liquid crystal display. As a light source of the external light, a backlight provided on the back surface of the liquid crystal display is used. Backlights have conventionally been served by cold-cathode tubes. In these days, however, there are circumstances when light emitting diodes (LEDs) are used instead of cold-cathode tubes because of the long lives, good color producibility, or the like thereof
In recent years, nano-size quantum dot phosphors are being commercialized under the initiative of overseas venture-capital organizations. Quantum dots are luminous semiconductor nanoparticles with a size in the range of 1 to 20 nm. The quantum dots with unique optical and electronic properties are on their way to being used in a large number of applications, such as flat panel displays, colorful illuminations (decorative lighting) and the like, in addition to the applications to fluorescence imaging in the fields of biology and medical diagnosis.
The white LED technique that is extremely important for displays typically uses a method of exciting cerium-doped YAG (yttrium aluminum garnet) down-conversion phosphors by using a blue (450 nm) LED chip. When blue light of an LED is mixed with yellow light of a wide wavelength range emitted from YAG phosphors, white light is produced. However, this white light is slightly bluish in many cases, and often taken to be cold or cool white light.
Quantum dots, which exhibit a wide excitation spectrum and have high quantum efficiency, are used as LED down-conversion phosphors (LED wavelength conversion phosphors). Moreover, only a change in the dot size or the type of the semiconductor material can fully adjust the wavelength of light emission throughout the visible range. Thus, quantum dots practically have a potential of producing any color, specifically a warm white color which has been strongly desired in the illumination industries. In addition to this, by combining three types of dots whose light emission wavelengths respectively correspond to red, green and blue, white lights with different color rendering indexes can be obtained. In this way, displays using backlights formed of quantum dots can improve hues to provide up to 65% of colors that can be recognized by persons, without increasing the thickness, power consumption, cost, the number of fabrication processes, and the like, compared with conventional liquid crystal TVs.
Such a backlight is formed by dispersing, inside a film, quantum dots having a light emission spectrum of red or green, and sealing both surfaces of the film with a barrier film or a laminate of barrier films. In some cases, the edge portions of the film are also sealed. The field of optical devices, for example, has been suffering from a problem of Newton's rings which are caused by members, such as a plastic film and a glass plate, which are in intimate contact with each other.
On the other hand, besides barrier properties, a barrier film used for sealing is required to have an appearance, transparency or the like conquering flaws or wrinkles. The term barrier film herein refers to a thin film that is formed on a surface of a base material, such as a plastic film, by vapor deposition or the like, and prevents gases or moisture from permeating therethrough. However, conventional barrier films have been served by those films which are used as packaging materials for foods, medical supplies, electronic devices and the like. Therefore, these barrier films can fail to provide satisfactory performance.
Thus, barrier films have suffered from splashes, foreign matters, or the like. The term splash herein refers to a phenomenon in which a material in the form of fine particles and at a high temperature to be vapor deposited scatters, or a phenomenon in which a material to be vapor deposited attaches to a base material and remains as foreign matters or makes a hole in the base material. In other words, barrier films for use in backlights have an issue of preventing the adverse effects of splashes and improving barrier properties.
Some methods can be proposed to cope with the above issue.
For example, Patent Literature 1 proposes an anti-Newton's ring sheet in which one surface or both surfaces of a member are roughened to prevent occurrence of Newton's rings. The roughening process as proposed includes sandblasting a surface of the member, or forming an anti-Newton's ring layer made of a binder component and fine particles on the member, or the like.
Patent Literature 2 proposes a backlight sandwiched between barrier films to prevent deterioration of the phosphors.
Patent Literature 3 proposes that an organic EL device is covered with a barrier film to ensure reliability of the organic EL device.